1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to an organic electroluminescent (EL) display device and a method of encapsulating the same.
2. Description of Related Art
Examples of a flat panel display device include a liquid crystal display (LCD) device, an organic EL display (OELD) device, a field emitter display (FED) device, and a plasma display panel (PDP). Of these, the organic EL display device attracts attention due to a wide viewing angle, a clearer moving picture, a high durability, and a high temperature resistance.
FIG. 1 is a cross-sectional view illustrating a conventional organic EL display device. The organic EL display device includes an organic EL element 18 including a lower electrode 12, an organic EL layer 14, and an upper electrode 16 which are sequentially stacked on a transparent insulating substrate (“insulating substrate”) 10.
A structure that emits light from the organic EL layer 14 toward the insulating substrate 10 is referred to as a back surface light emitting structure, and a structure that emits light from the organic EL layer 14 toward a direction opposite to the insulating substrate 10 is referred to as a front surface light emitting structure.
In case of the back surface light emitting structure, the lower electrode 12 is made of a transparent conductive material, and the upper electrode 16 is made of an opaque conductive material. On the other hand, in case of the front surface light emitting structure, the lower electrode 12 is made of an opaque conductive material, and the upper electrode 16 is made of a transparent conductive material.
Hereinafter, the organic EL display device is described focusing on the back surface light emitting structure.
The lower electrode 12 is made of a transparent conductive material including one of indium tin oxide (ITO) and indium zinc oxide (IZO), and the upper electrode 16 is made of an opaque conductive material including one of magnesium, aluminum, indium, and silver-magnesium.
A passivation layer (not shown) can be formed over the entire surface of the insulating substrate 10 to cover the organic EL element 18.
A metal cap 20 is attached to the insulating substrate 10 using an adhesive 22 to encapsulate the organic EL element 18 so as to protect the organic EL display from oxygen or moisture. The metal cap 20 is made of an aluminum alloy. A moisture/water absorbing layer 24 is arranged on an inner surface of the metal cap 20 to prevent element characteristics (e.g., a light-emitting efficiency) from being deteriorated due to the moisture or water.
FIG. 2 shows a flow chart illustrating a process of encapsulating the organic EL display device of FIG. 1. The lower electrode 12, the organic EL layer 14, and the upper electrode 16 are sequentially formed on the insulating substrate 10 (operation 202). The adhesive 22 is coated on a periphery region of the insulating substrate 10 to a thickness of about 150 μm (operation 204). The metal cap 20 is rested on the adhesive 22 and pressurized to attach the metal cap 20 to the insulating substrate 10 (operation 206). The adhesive 20 is cured at a predetermined temperature using a UV light (operation 208). Accordingly, encapsulation of the organic EL element 18 is completed.
However, the conventional encapsulating method has at least the following problems. As the adhesive 22 is pressurized by the metal cap 20, the thickness of the adhesive 22 is reduced to ˜50 μm. Therefore, an inner pressure of a space formed by the insulating substrate 10 and the metal cap 20 is increased. Also, as the adhesive 22 is cured using a UV light, a gas volume of the space causes a thermal expansion. As a result, the adhesive 22 can be separated from the insulating substrate 10 and can have a non-uniform width. Accordingly, moisture can leak into the space, thereby deteriorating element characteristics of the organic EL display device.
In addition, the conventional organic EL display having the structure described above cannot satisfy a current trend toward a compact display device.